If we choose to live near convergent plate boundaries, we can build buildings that can resist earthquakes, and we can evacuate areas around volcanoes when they threaten to erupt. Yes, convergent boundaries are dangerous places to live, but with preparation and watchfulness, the danger can be lessened somewhat.
Nitrification, as stated above, is formally a two-step process; in the first step ammonia is oxidized to nitrite, and in the second step nitrite is oxidized to nitrate. Different microbes are responsible for each step in the marine environment.
1 Step One The first thing that happens when you put fish in the tank is ammonia is produced. This is from the fish waste or excess foods that are decomposing.  Step Two As the amount of ammonia starts to increase, a bacteria forms called nitrosomonas. This bacteria begins to convert the ammonia into nitrite.